This invention relates to transparent sheet materials. More particularly it relates to transparent sheet materials which have an ink-receptive stratum thereon.
Transparent sheet materials are commonly employed to prepare "visual transparencies." Such transparencies are utilized to project graphic images onto a viewing surface such as a screen or a wall.
One technique for preparing transparencies involves depositing an ink composition on the sheet material in image areas. This technique is especially useful when it is desired to automatically print information stored in data banks or other memory devices and utilizing devices such as computer graphic plotters.
The applicator pens used to deposit the ink compositions are frequently exposed to air for extended periods of time. Consequently, the ink compositions utilize solvents of low volatility (e.g., water, formamide, ethylene glycol monoethyl ether, etc.) to retard drying of the pen tips.
Several drawbacks exist with respect to the transparent films presently utilized to prepare visual transparencies. For example, many of the films do no accept inks (i.e., the ink composition balls up on the film surface). Those films that do accept the ink do not permit it to dry quickly but rather require extended period of time (e.g., 3 minutes or more) before the ink dries thereon. This greatly increases the opportunity for the image to be smeared and significantly reduces the plotter's speed. Still further, many of the films presently utilized show fingerprints badly. This greatly detracts from the esthetic quality of the final transparencies and makes the projected image less well defined.
The present invention, however, represents a dramatic improvement over the prior art. It provides transparent sheet materials which readily accept a wide variety of ink compositions (even those that employ low volatility solvents such as water, formamide and ethylene glycol monoethyl ether) and permits the ink compositions to dry quickly. Thus the sheet materials of the invention permit the ink to dry in 30 seconds or less and preferably in 10 seconds or less. Consequently, transparencies made from the film structure of the invention can be handled and stored in stacks almost immediately after preparation. Additionally the sheet materials of the invention exhibit improved resistance to fingerprinting. Still further the images produced on the sheet materials of the invention are strong in color and have excellent edge acuity. The preferred sheet materials of the present invention also exhibit good room temperature shelf stability. That is, they are not significantly affected by storage under such conditions.